>Thanks. I think the term "Component" was confusing me, I thought it was >related to the components of a field. I think this would be useful to me >if I wanted to assign coordinates to the vertices, wouldn't it?
Yes. You can put whatever data you want in the component data structure. > >Also, I was wondering how to set up dirichlet boundary conditions, >basically fixing certain nodes position. > > > You can add a component at each node with a field marking whether the node is a boundary node. >Could I do it as the function SetInitialValues does it in the pflow >example? > No. You need to put in the component data structure before calling DMNetworkAddComponent() >These values are used to eliminate the zeroth-order energy modes of the >stiffness matrix? > > >Last question, in my case I have two degrees of freedom per node, when I >grab the offset with DMNetworkVariableOffset, that's for the first degree >of freedom in that node and the second degree of freedom would just be >offset+1? > Yes. Shri > >Miguel > > >On Wed, Sep 24, 2014 at 9:52 PM, Abhyankar, Shrirang G. ><abhy...@mcs.anl.gov> wrote: > >If you have equations only at the nodes, with a part of it contributed by >the edges (springs), then you can use DMNetwork. If you are planning to >have equations for the beads in the future, or other higher layers, then >DMPlex has better functionality > to manage that. > >Shri > > >From: Miguel Angel Salazar de Troya <salazardetr...@gmail.com> >Date: Wed, 24 Sep 2014 17:38:11 -0500 >To: Shri <abhy...@mcs.anl.gov> >Cc: "petsc-users@mcs.anl.gov" <petsc-users@mcs.anl.gov> >Subject: Re: [petsc-users] DMPlex with spring elements > > > > > >Thanks for your response. I'm attaching a pdf with a description of the >model. The description of the PetscSection is necessary for the >DMNetwork? It looks like DMNetwork does not use a PetscSection. > > > > > > >Miguel > > >On Wed, Sep 24, 2014 at 1:43 PM, Abhyankar, Shrirang G. ><abhy...@mcs.anl.gov> wrote: > > >>Thanks for your response. My discretization is based on spring elements. >>For the linear one dimensional case in which each spring has a >>coefficient k, their jacobian would be this two by two matrix. >>[ k -k ] >>[ -k k ] >> >>and the internal force >> >>[ k ( Ui - Uj) ] >>[ k ( Uj - Ui) ] >> >>where Ui and Uj are the node displacements (just one displacement per >>node because it's one dimensional) >> >>For the two dimensional case, assuming small deformations, we have a >>four-by-four matrix. Each node has two degrees of freedom. We obtain it >>by performing the outer product of the vector (t , -t) where "t" is the >>vector that connects both nodes in a spring. This is for the case of >>small deformations. I would need to assemble each spring contribution to >>the jacobian and the residual like they were finite elements. The springs >>share nodes, that's how they are connected. This example is just the >>linear case, I will have to implement a nonlinear case in a similar >>fashion. >> >>Seeing the DMNetwork example, I think it's what I need, although I don't >>know much of power electric grids and it's hard for me to understand >>what's going on. Do you have a good reference to be able to follow the >>code? > >> >Please see the attached document which has more description of DMNetwork >and the equations for the power grid example. I don't have anything that >describes how the power grid example is implemented. > >>For example, why are they adding components to the edges? >> >>475: DMNetworkAddComponent >><http://www.mcs.anl.gov/petsc/petsc-as/petsc-current/docs/manualpages/DM/ >>D >>MNetworkAddComponent.html#DMNetworkAddComponent>(networkdm,i,componentkey >>[ >>0],&pfdata.branch[i-eStart]);Miguel > >Each edge or node can have several components (limited to 10) attached to >it. The term components, taken from the circuit terminology, refers to the >elements of a network. For example, a component could be a resistor, >inductor, spring, or even edge/vertex weights (for graph problems). For >code implementation, component is a data structure that holds the data >needed for the residual, Jacobian, or any other function evaluation. In >the case of power grid, there are 4 components: branches or transmission >lines connecting nodes, buses or nodes, generators that are incident at a >subset of the nodes, and loads that are also incident at a subset of the >nodes. Each of the these components are defined by their data structures >given in pf.h. > >DMNetwork is a wrapper class of DMPlex specifically for network >applications that can be solely described using nodes, edges, and their >associated components. If you have a PDE, or need FEM, or need other >advanced features then DMPlex would be suitable. Please send us a write-up >of your equations so that we can assist you better. > >Shri > > >> >> >>On Tue, Sep 23, 2014 at 11:13 PM, Abhyankar, Shrirang G. >><abhy...@mcs.anl.gov> wrote: >> >>You may also want to take a look at the DMNetwork framework that can be >>used for general unstructured networks that don't use PDEs. Its >>description is given in the manual and an example is in >>src/snes/examples/tutorials/network/pflow. >> >>Shri >> >>From: Matthew Knepley <knep...@gmail.com> >>Date: Tue, 23 Sep 2014 22:40:52 -0400 >>To: Miguel Angel Salazar de Troya <salazardetr...@gmail.com> >>Cc: "petsc-users@mcs.anl.gov" <petsc-users@mcs.anl.gov> >>Subject: Re: [petsc-users] DMPlex with spring elements >> >> >>>On Tue, Sep 23, 2014 at 4:01 PM, Miguel Angel Salazar de Troya >>><salazardetr...@gmail.com> wrote: >>> >>>Hi all >>>I was wondering if it could be possible to build a model similar to the >>>example snes/ex12.c, but with spring elements (for elasticity) instead >>>of >>>simplicial elements. Spring elements in a grid, therefore each element >>>would have two nodes and each node two components. There would be more >>>differences, because instead of calling the functions f0,f1,g0,g1,g2 and >>>g3 to build the residual and the jacobian, I would call a routine that >>>would build the residual vector and the jacobian matrix directly. I >>>would >>>not have shape functions whatsoever. My problem is discrete, I don't >>>have >>>a PDE and my equations are algebraic. What is the best way in petsc to >>>solve this problem? Is there any example that I can follow? Thanks in >>>advance >>> >>> >>> >>> >>>Yes, ex12 is fairly specific to FEM. However, I think the right tools >>>for >>>what you want are >>>DMPlex and PetscSection. Here is how I would proceed: >>> >>> 1) Make a DMPlex that encodes a simple network that you wish to >>>simulate >>> >>> 2) Make a PetscSection that gets the data layout right. Its hard from >>>the above >>> for me to understand where you degrees of freedom actually are. >>>This is usually >>> the hard part. >>> >>> 3) Calculate the residual, so you can check an exact solution. Here >>>you >>>use the >>> PetscSectionGetDof/Offset() for each mesh piece that you are >>>interested in. Again, >>> its hard to be more specific when I do not understand your >>>discretization. >>> >>> Thanks, >>> >>> Matt >>> >>> >>>Miguel >>> >>> >>> >>>-- >>>Miguel Angel Salazar de Troya >>>Graduate Research Assistant >>>Department of Mechanical Science and Engineering >>>University of Illinois at Urbana-Champaign >> >> >>>(217) 550-2360 <tel:%28217%29%20550-2360> >>>salaz...@illinois.edu >>> >>> >>> >>> >>> >>> >>> >>> >>> >>>-- >>>What most experimenters take for granted before they begin their >>>experiments is infinitely more interesting than any results to which >>>their experiments lead. >>>-- Norbert Wiener >> >> >> >> >> >> >> >> >> >>-- >>Miguel Angel Salazar de Troya >>Graduate Research Assistant >>Department of Mechanical Science and Engineering >>University of Illinois at Urbana-Champaign >>(217) 550-2360 >>salaz...@illinois.edu > > > > > > > > > >-- >Miguel Angel Salazar de Troya >Graduate Research Assistant >Department of Mechanical Science and Engineering >University of Illinois at Urbana-Champaign >(217) 550-2360 >salaz...@illinois.edu > > > > > > > > > > > > > >-- >Miguel Angel Salazar de Troya >Graduate Research Assistant >Department of Mechanical Science and Engineering >University of Illinois at Urbana-Champaign >(217) 550-2360 >salaz...@illinois.edu
